1. Field of the Invention
The invention relates to a bag able to preserve a product in powder form under sterile conditions and to enable a liquid to be fed into the bag to form therein a sterile solution of the product.
2. Description of the Background
Many products obtained in sterile form in the solid state are known to be used in the liquid state as sterile solutions, suspensions, dispersions, or the like.
A typical example is a pharmaceutical product such as an antibiotic or vitamin, or a culture medium for micro-organisms such as cells, bacteria or moulds which at the moment of use are dissolved or dispersed in liquid.
The problem of dissolving or dispersing a sterile powder in liquid while maintaining sterility is considerable and costly, and is solved in various ways, all involving problems which are summarized below by referring to two particularly important cases.
For example, cell culture medium is produced in the form of powder which can be sold as such in polyethylene bags or bottles closed with a screw stopper. To be used, this product is dissolved in liquid to form a solution (typically an amino acid, electrolyte or vitamin solution) in a totally septic environment, this involving time and considerable cost.
The sterile solution obtained in this manner is fed into a glass jar or bottle in a suitable sterile bottling environment, and the sealed bottle is despatched to the client in a special housing and protection container. The user has then to open the bottle under aseptic conditions to be able to then withdraw the solution contained in it.
This method is well known, and is explained for example in lines 9–59 of column 1 of the U.S. Pat. No. 4,910,147.
To solve these problems, U.S. Pat. No. 4,910,147 proposes to sell to the user not the product, but instead an already prepared sterile solution of the cell culture medium enclosed in a sealed flexible bag, into which the solution is fed using semi-automatic aseptic filling machines. Such bags, which are completely filled with the solution, are much more manageable than glass bottles and can be easily and economically despatched by the producer to the user who, without the need for a special apparatus or a sterile environment, can directly withdraw all or part of the sterile solution through one or more ports with which the bag is provided.
However, this system also presents problems because although it is relatively simple to store and transport small bags filled with liquid, in the case of bags containing a relatively large liquid volume, for example five liters or more, the hydraulic force exerted by the liquid during transport can break the bag, as is clearly explained in lines 34–50 of column 1 of U.S. Pat. No. 4,968,624, which names the same inventors and the same proprietor as U.S. Pat. No. 4,910,147.
For this reason U.S. Pat. No. 4,968,624 describes a very complex rigid structure within which the bags containing the solutions have to be enclosed for their storage and transport.
Again for example, reference can be made to the method of using those sterile crystalline antibiotics (in powder form) contained in single-dose form in glass bottles sealed by rubber plugs. To make such antibiotics injectable into a patient by using a syringe a sterile solvent (water) is drawn from a vial (which firstly is broken or opened), then the solvent is fed into the bottle by piercing its plug with the syringe needle, the bottle is shaken to dissolve the antibiotic powder, and the solution formed in this manner is drawn into the syringe through the needle which passes through the plug of the bottle, after which the solution can be injected into the patient.
Although this operation may be relatively simple to carry out by a user who has to prepare the solution and inject it only one or a few times a day, it becomes very demanding and costly in hospitals in which specialized personnel (nurses) have to repeat the same operation a very large number of times every day, with considerable time wastage, high cost and serious problems of maintaining sterility, these being enhanced by the need to dispose of a large number of empty glass bottles with rubber plugs, glass vials and miscellaneous packaging material.
Again it should be noted that it is not possible to prepare solutions of antibiotics (for example in bags such as those described in U.S. Pat. No. 4,910,147 and in U.S. Pat. No. 5,364,384) in suitable plants to then despatch them to hospitals, because such solutions remain unaltered only for a very short time, and then only if special care is taken for their preservation.
In order to solve the above mentioned problems the U.S. Pat. No. 5,484,431 has proposed the use of a bag constructed from a flexible polyolefin material, sealed at its periphery and defining a closed sterile space containing a sterile solute or a soluble product in powder form occupying only a minor portion of the capacity of the bag.
The bag has a plurality of ports through which a liquid can be introduced into it for dissolving the powder or solute and respectively for withdrawing the solution which has been formed within the bag.
According to the teachings of the U.S. Pat. No. 5,484,431 the amount of liquid introduced into the bag is such to completely fill it as it is stated, for example, in line 62 of col. 8 and line 23 of col. 9 of the patent specification: in order to make it possible to dissolve the powder or solute contained therein, the bag must include internal means for creating turbulence within its interior (see lines 1–3 of col. 3): preferably the bag is provided with an internal seal 14 (see lines 43–45 and 56–60 of col. 4) which functions to create turbulence when the liquid flows into the bag ensuring an adequate mixing of the liquid and the powder or solute in order to create a solution.
Such solutions are for intravenous administration of dextrose solutions, saline, lactated Ringer's or the like whose concentrations in the respective solutions need not be exactly predetermined and the same in each bag.
The structure of the bag disclosed in the U.S. Pat. No. 5,484,431 is not a simple one, because it must comprise internal means for creating turbulence within its interior as a consequence of the fact that the liquid introduced therein completely fills the bag, so that a simple shaking of the bag would practically be ineffective to completely dissolve the powder or the solute. Moreover, since the bags are formed with a flexible sheet of plastic materials and the bags are completely filled with the liquids introduced therein, it is impossible to obtain solutions all having the same preestablished concentration of the materials dissolved therein.
Finally, the solutions formed in the bags are used for intravenous administration, where it is not necessary to exactly control the amount of the active substances which are administered to the patients.